Method for determining the position of a first moving component relative to a second component and device for applying said method

ABSTRACT

A method for determining the position of one of two components in relative motion with respect to each other, using optical means, comprises:
         directing at least one light beam emitted by a light source attached to one component towards a diffractive support attached to the second component, calculated and manufactured for generating an optical signal indicative of the positioning of said support, the optical signal being produced by the diffractive support in transmission and/or in reflection, and the optical signal including information indicative of its quality;   detecting and reading at least one optical code formed by said signal, which corresponds to a unique position of the diffractive support relatively to the beam; and   assigning a position to each detected optical code.

TECHNICAL FIELD

The present invention relates to the general technical field of systemsor devices allowing a relative movement between two components to bedetermined and measured, for example a displacement between a mobilepart and a fixed part.

BACKGROUND OF THE INVENTION

In an increasing number of technical applications, it has becomeimportant to be able to accurately give the position of a mobilecomponent relatively to a fixed mark for example, occasionally at a highfrequency. Such is the case for example in a vehicle steering column orin machine tools performing complex machining operations, or even, againin the automotive field, for flaps of air-conditioning systems. Thepossible applications are countless and explain the exponentialdevelopment of positioning sensors, in particular linear or angularsensors.

In fact, one of the driving factors influencing the demand for sensorshaving improved resolution is the anticipated development ofelectronically controlled steering systems, in which systems, safety iscritical. In such systems, sensors must perform with extremely highreliability, often requiring redundancy in many forms. In these systems,the effect of an error in reported position can be dangerous, and thesensor must be able to self-diagnose when an error has occurred.

Several technologies may be used for detecting and measuring relativepositions, the sensors which stem from the latter being, in most cases,associated with complex electronic processing means using interpolationalgorithms which allow the position to be calculated.

Devices for locating a position relatively to a fixed mark, are thusalready known, based on optical technologies, which however require,under nearly all assumptions, complex electronic processing of verybasic optical information.

SUMMARY OF THE INVENTION

The aforementioned goals, and other advantages, are achieved by thepresent invention, which relates to a method for determining theposition of one of two moving components relatively to each other,consisting of:

-   -   directing at least one light beam emitted by a light source        attached to one component, towards a diffractive support        attached to the second component, wherein the support is        calculated and manufactured in order to generate a diffracted        optical signal indicative of the positioning of said support,        wherein the optical signal is produced by the diffractive        support in transmission and/or in reflection, and wherein the        optical signal includes information indicative of its quality;    -   detecting and reading at least one optical code formed by said        signal, which corresponds to a unique position of the        diffractive support relatively to the beam and which code        includes information indicative of the quality of the signal;    -   assessing the quality of the signal; and    -   assigning a position to each detected optical code.

The originality of this method, based on phase and/or amplitudemodulation of the incident signal, lies in the fact that the coding isachieved by optical means, which notably provides simplification ofelectronic processing. The relative positions of the moving componentsmay simply be coded in an absolute way. This invention proposes toinclude a level of redundancy in the encoding of the information on thedisk itself, in the form of error detecting (parity) or error detecting& correcting (cyclic redundancy check) codes that are embedded with theposition information. Thus, an error detecting code would facilitate anassessment of signal quality or reliability, and if desired, detectionand/or correction of errors that could occur at one or more points inthe system.

Diffractive optical coding further has advantages which are alsoexpressed in the devices for applying the method, and which will bementioned in more detail in the following text.

According to an exemplary embodiment of the method, the optical signalmay be defined by the first diffraction order, the complementary signalsin the same diffraction order being however retained in order tomaintain the intensities of the detected light spots substantiallyconstant. Interpretation errors are thereby avoided, related to anon-constant intensity of the spots to be detected and to be analyzed.Uniformization of the diffracted energy resulting from this facilitatesthe reading of the position which consequently is more reliable. Aportion of the diffractive portion is read, and the complementaryportion in the same diffraction order is not read, but used forcounter-balancing the excess energy in order to uniformize theintensity.

According to an alternative, the conjugate order corresponding to thefirst diffraction order, may however also be read and compared with thelatter. With this, it is possible to carry out a check of the opticalcode obtained by reading the first diffraction order, as there isredundancy between both pieces of information.

Other diffraction orders may however be used, for specifying, completingor checking the read-out of the optical signals.

In an exemplary embodiment, the information that is indicative of thequality of the signal may include error detecting and correcting codessuch as parity codes, information facilitating checksum operations, andinformation facilitating polynomial redundancy checks. For example,parity (even or odd) codes enable the counting of the quantity of “ones”in a word, and a parity code is indicative of whether there are an evenor odd number of “ones.” In an embodiment utilizing a parity code as anindication of quality, the receiving system may count the number of onesand compare the resulting count to the parity bit. In such a system, adisagreement may indicate an error and thus the system may assess thesignal as unreliable (i.e., exhibiting poor quality). It should be notedthat this method can detect single-bit errors and some multiple biterrors, but may be unable to correct the signal or otherwise improve itsquality without additional means for doing so.

The information that is indicative of the quality of the signal may alsoinclude information facilitating checksum operations. Checksums can beused on groups of data words wherein the sum of the data words iscalculated and stored with the data. In such systems, the receivingsystem calculates the same checksum and compares it with the receivedchecksum. In such a system, a disagreement may indicate an error andthus the system may assess the signal as unreliable (i.e., exhibitingpoor quality).

The information that is indicative of the quality of the signal may alsoinclude information facilitating cyclic redundancy checks usingpolynomials. In such systems, complex polynomials may be utilized thatcan not only detect, but in some cases correct, single- or multiple-biterrors.

Preferably, the position corresponding to the last detection is stored.If need be, this allows anomalous movements to be detected, for exampleoccurring during failure or deterioration of a mechanical part involvedin the movement or in the determination of the position.

The optical code formed by each optical signal in the case in pointappears as optical structures, on the base of which bits 0 and 1 of anelectronic code are generated by means for detecting and reading saidstructures. Such an optical signal is extremely interesting as it isinsensitive to vibrations, offsets (for example, it is translationallyinvariant with a Fourier diffractive support).

According to an alternative in which the codes are not distinguished persectors according to the positions of the mobile component, but theychange rather continuously, each detected and read signal is submittedto an algorithm for calculating the position of the diffractive supportrelatively to the beam. Of course, the algorithm changes according tothe relative displacement velocity.

In the method of the invention, according to another alternative, eachdetected and read optical code is compared with electronic codes storedin a memory table and which allow the position of the diffractivesupport to be determined on a one-to-one basis. Each code in factcorresponds to a unique position. It then needs to be identified, i.e.,each code needs to be delimited in practice.

For this purpose, the diffractive optical code may include at least onestarting optical structure and at least one end optical structuredelimiting the read-out area of the optical signal corresponding to adetermined position of the diffractive support relatively to the beam.

According to an additional possibility, each optical code correspondingto a position of the diffractive support may include at least oneoptical synchronization structure, the detection of which allows thetriggering of the read-out phase for the optical signal integrating thecode of a position of the diffractive support relatively to the beam.This phase is then only carried out when the delimitation of the code isconfirmed by the optical synchronization signal.

In an exemplary embodiment, a method includes the step of assessing thequality of the optical signal and/or of the position informationinterpreted from the optical signal. In another exemplary embodiment, amethod includes the further step of correcting the position informationto create a position signal having improved reliability.

In an exemplary embodiment, a system employing the described methodincludes means for assessing the quality of the optical signal and/or ofthe position information interpreted from the optical signal. In anotherexemplary embodiment, a system employing the described method includesmeans for correcting the position information to create a positionsignal having improved reliability.

For the aforementioned alternatives, each optical code corresponding toan identifiable position may finally include at least one opticalcalibration structure used for the purpose of diagnosing proper read-outoperation.

Said optical structures in fact consist of at least one light spot, theintensity of which may be measured. In the case of operational failureof the components of the system, or appearance of conditions(condensation, . . . ) causing uncertain operation, the analysis ofthese optical structures and of the signal which they form, allows thesystem to conclude as to whether an adequate read-out is possible ornot.

It should be noted that the light spot forming the optical structure mayassume different, more or less complex shapes.

According to one possibility, the codes defining the position of acomponent relatively to the other comply, in the order of theirsuccession, with the GRAY code. The change of a single light spot at aknown location therefore provides considerable simplification of thepositioning analysis.

The changes in intensity of at least one of the optical structuresforming the optical signals may further be coded by an analog/digitalconverter, authorizing a binary or grey-level read-out with which theresolution of the measurement may be further refined.

In the case of sectorized coding, which corresponds to the firstaforementioned alternative, the light source may be pulsed according toa frequency controlled by the velocity of the moving component, theread-out being then synchronized with the generation of the lightbeam(s). With this, if need be, the use of an optical synchronizationsignal may be omitted.

The method reported above may be applied to any type of relative motion,and notably to relative rotation of two components. Under thisassumption, it consists of determining the angular position of one ofthe components relatively to the other.

The accuracy of the measurement depends on dimensional, manufacturingconsiderations, and also obviously on the desired definition for thesignal: according to one possibility, the number of optical spots orstructures used for coding the angular position, is at least equal to 12to provide an angular resolution less than 0.1° and an accuracy of thesame order of magnitude. The 4,096 possibilities provided by 12 bitsactually allow a resolution of this order.

The object of the present invention is also achieved by a diffractivesupport including mounting means on a first component in relative motionwith respect to a second component, and provided with at least onediffractive track, either continuous or not, said diffraction trackhaving means for diffracting by reflection and/or by transmission, thelight beam emitted by at least one light source, fixed with respect tothe second component.

The diffraction of the light rays may be obtained via different routes.

Thus, the diffractive track may for example have an etched relief in theconstituent material of the diffractive support, capable of diffractingthe incident beam(s) and of generating an optical signal, the reading ofwhich allows the position of the first component relatively to thesecond component to be identified, by identifying the code formed by thesignal.

According to a second exemplary embodiment, the diffractive track may beobtained by modulating the transparence of the support, for example byapplying an opaque material onto certain locations on a transparentsupport, to obtain the same result.

The diffractive track may also be obtained by modulating the refractiveindex or even by a combining the mentioned solutions.

For example, modulation of the reliefs or of the opaque material, thegeometry and the distribution of which are calculated by a computer,generates a particular diffracted optical signal under the action of atleast one light beam, said signal forming an optical code consisting ofoptical structures defining a unique position of the support at anytime.

The diffractive support may thus be made with known materials, withlarge reproducibility and without altering the accuracy and/or theresolution of the determination of each position. Large importance isattached to the selection of these materials, which preferably should beinexpensive and easy to machine. For example, they may be polycarbonate,PMMA, and more generally all optically adequate materials.

According to an exemplary embodiment corresponding to one of theaforementioned alternatives, each track is divided into areas with anindividualized diffractive structure generating a code corresponding toa unique position of the support, each area including a plurality ofelementary shapes with a parallelogrammic aspect, positioned as aperiodic or aperiodic grid.

In a rotary configuration, the diffractive support may for exampleinclude:

-   -   a rigid disk;    -   means for mounting to a rotary shaft;    -   at least one ring-shaped diffractive track.

As an example, the disk may include three diffractive tracks, the firstone being used for defining the optical code, the second one being usedfor defining a synchronization signal and the third one being used fordefining a calibration signal.

Under the assumption of the first alternative with sectorized domains,as mentioned above, each track is then divided into angular sectors withequal surfaces, delimiting said individualized diffractive structures.

According to an exemplary embodiment observing the requirements forreduced bulkiness, the angular sectors may have dimensions of the orderof 10 μm to 100 μm. The dimensions of the disk are then provided so thateach track comprises at least 3,600 angular sectors, so as to meet therequirement of a resolution less than 0.1°.

By meeting these assumptions, it is possible to build a support, theradius of which does not exceed a few tens of millimeters.

The disk is not necessarily flat, and it may include, on its periphery,a tapered portion, one of the tilted surfaces of which includes at leastone diffractive track. With such a tilted surface, it is possible forexample, to optimize the positioning and/or the orientation of the lightsource and of the detection means.

According to another exemplary embodiment, very flexible to use, thediffractive track may be positioned on a cylindrical surface, forexample the rotary shaft of a steering column. Bonding of a diffractivetrack thereon, the support of which is flexible, may then becontemplated.

The object of the present invention is also achieved by a device formeasuring the position of a first component in relative motion withrespect to a second component and including:

-   -   at least one fixed light source, emitting at least one light        beam on at least one mobile diffractive support;    -   means for detecting and reading an optical signal obtained by        diffraction of the light beam(s) by transmission or reflection        from the diffractive support(s), said optical signal including        information indicative of its quality;    -   and means for processing the optical code resulting from the        detected signal with which the position of the diffractive        support(s) and quality or reliability of the position        information may be determined relatively to the beam(s);    -   means for assessing the quality of the optical signal and/or the        position information; and    -   means for optionally correcting the position information to        produce position information having improved quality and/or        reliability.

In an exemplary embodiment, the information that is indicative of thequality of the signal may include error detecting and correcting codessuch as parity codes, information facilitating checksum operations, andinformation facilitating polynomial redundancy checks. For example,parity (even or odd) codes enable the counting of the quantity of “ones”in a word, and a parity code is indicative of whether there are an evenor odd number of “ones.” In an embodiment utilizing a parity code as anindication of quality, the receiving system may count the number of onesand compare the resulting count to the parity bit. In such a system, adisagreement may indicate an error and thus the system may assess thesignal as unreliable (i.e., exhibiting poor quality). It should be notedthat this method can detect single-bit errors and some multiple biterrors, but may be unable to correct the signal or otherwise improve itsquality without additional means for doing so.

The information that is indicative of the quality of the signal may alsoinclude information facilitating checksum operations. Checksums can beused on groups of data words wherein the sum of the data words iscalculated and stored with the data. In such systems, the receivingsystem calculates the same checksum and compares it with the receivedchecksum. In such a system, a disagreement may indicate an error andthus the system may assess the signal as unreliable (i.e., exhibitingpoor quality).

The information that is indicative of the quality of the signal may alsoinclude information facilitating cyclic redundancy checks usingpolynomials. In such systems, complex polynomials may be utilized thatcan not only detect, but in some cases correct, single- or multiple-biterrors.

Preferably, this position-measuring device includes means for storingthe obtained position, so as to use it in the subsequent processing ofthe information for example.

Without this being a necessity, the incident beam is preferably obtainedfrom a coherent light source, for example a laser diode.

The optical circuit used may comply with multiple configurationsaccording to the application and to constraints, for example instructures or in bulkiness.

The light beam(s) may thus be sent towards the diffractive support(s)via at least one relay optical component of the mirror, lens, prism,diffractive component, reflective component, refractive component type,and/or via at least one optical guiding component of the optical fiberor waveguide type, the object being the optimization of the positioningand bulkiness of the whole of the constituent components of themeasuring device. Optical components as mentioned may also be used atthe output of the diffractive support(s).

Said light beam(s) may, depending on the case, also pass through atleast one unit exerting a collimating, focusing or astigmatism function.The dimensions of each light beam may thereby be adapted to the size ofthe individualized diffractive structures.

Under certain assumptions, the light beam(s) may further be sent to thediffractive support(s) via at least one conformation diaphragm.Illumination of the adjacent diffractive structures which may generateerroneous codes or parasitic interferences is thereby avoided.

According to one possibility, the means for detecting and reading thediffracted optical codes may consist of photodetectors of the arraystrip, grid or pixel matrix type, CCD sensors, photodiodes, or evenphotoelectric or photovoltaic cells, positioned on the trajectory of therays diffracted by the diffractive support(s). The number and thearrangement of the pixels or sensors are defined, according to theapplication, depending of the accuracy and/or the rapidity which theinformation processing should achieve.

According to a possible configuration, the photodetectors may bepositioned so that each optical spot or structure obtained at thelocation where a diffracted ray encounters a pixel array, covers atleast 3 pixels. With this, the obtained optical signals may be betterdetected. Conversely, a gain in processing rapidity may be obtained bydetection with only one cell.

Also, the number of pixels between two adjacent spots is set to at leastthree pixels. Practically, the detection unit is a photodetectorcomponent which exists on the market.

In certain configurations, the light beam(s) are directed at anincidence normal to the diffractive support, although this may mean thatthis feature involves a more cumbersome optical circuit, i.e.,comprising more components than the relay optical components fordirecting the beam(s).

Conversely, if the light beam is tilted towards the diffractive support,preferably with an angle between 0° and 45° relatively to the normal,the circuit followed by the beam(s) may be simplified as the latter ismore directly turned towards the support.

The device may further include synchronization means for detecting andreading an optical code generated by an individualized diffractivestructure exclusively when the ray emitted by the light source iscentered on said structure for example.

According to an exemplary embodiment, synchronization means may includespecific photodetectors dedicated to detecting optical structuresobtained independently from those forming the code of the position to bemeasured, for example, light spots positioned on at least onediffractive track specifically dedicated to synchronization.

An application in which the different hitherto contemplated parts of theinvention are particularly of interest, is the measurement of the rotarymovement of at least a diffractive support permanently attached to arotary shaft.

In this case, in order to produce an absolute angle sensor over severalrevolutions, it is even possible to associate two superimposeddiffractive rotary disks, one including the measurement of angularposition on one revolution and the other, rotating N times slower,allowing the number of accomplished revolutions to be measured withinthe limit of N revolutions.

The present invention also relates to a method for calculating theposition of a component relatively to another one, from an opticalsignal generated by a diffractive support, said signal generating a codeconsisting of optical structures with variable intensity distributedover the detection means, the method consisting of:

-   -   detecting the status of each optical structure and assigning it        to an electronic state corresponding to its intensity;    -   calculating the value of the code of the measured position    -   assessing the quality of the optical signal;    -   converting said code into a linear or angular distance;    -   assessing the reliability of the distance; and    -   correcting the distance to produce a distance with improved        reliability.

As an example, the invention on the whole may perfectly be applied to asteering column of a vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages will also become apparent from thedetailed description appearing hereafter, with reference to the appendednon-limiting drawings, according to which:

FIG. 1 is a flow chart of an exemplary embodiment of the methodaccording to the invention;

FIG. 2 is a flow chart of an exemplary embodiment of a calculationmethod according to the invention;

FIGS. 3 a and 3 b are exemplary embodiments of a diffractive supportaccording to the invention;

FIGS. 4 a and 5 a are exemplary embodiments of details of diffractivetracks of a diffractive support according to the invention;

FIGS. 4 b and 5 b illustrate coded optical signals diffracted by thedetails of diffractive tracks of FIGS. 4 a and 5 a, respectively;

FIGS. 6-9 illustrate examples of coded optical signals and of theirprocessing during rotation of the diffractive support;

FIG. 10 illustrates an exemplary embodiment of a measuring deviceaccording to the invention;

FIG. 11 a illustrates a first alternative embodiment of the measuringdevice of FIG. 10;

FIG. 11 b illustrates a second alternative embodiment of the device ofFIG. 10;

FIG. 12 illustrates another exemplary embodiment of the measuring deviceaccording to the invention;

FIG. 13 illustrates another exemplary embodiment of the measuring deviceaccording to the invention;

FIG. 14 illustrates another exemplary embodiment of the measuring deviceaccording to the invention;

FIG. 15 illustrates another exemplary embodiment of the measuring deviceaccording to the invention;

FIG. 16 illustrates another exemplary embodiment of the measuring deviceaccording to the invention;

FIG. 17 illustrates another exemplary embodiment of a diffractivesupport according to the invention;

FIG. 18 is a schematic illustration of an exemplary embodiment of ameasuring device according to the invention;

FIG. 19 schematically illustrates details of the measuring device and ofthe diffractive support according to the invention;

FIG. 20 is an illustration of an exemplary diffracted optical signal,obtained from the method according to the invention;

FIG. 21 illustrates an enlarged detail from FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a method for determining the positionof one of two components in relative motion to each other. The methoduses optical means. For example an exemplary functional flow chart isschematized in FIG. 1.

The method according to the invention according to step (e₁) consists ofdirecting at least one light ray emitted by a light source onto adiffractive support (1) provided for generating an optical signal. Thelatter is indicative of the positioning of the support relatively to afixed mark. The optical signal is produced by the diffracted support (4)by transmission and/or by reflection.

According to a following step (e₂), the method consists of detecting andreading at least one constituent optical code of the signal. Thisdiffracted signal corresponds to a unique position of the diffractivesupport (1) and includes information indicative of its quality. Theoptical code according to step (e₃) is then compared via a memory tablewith prerecorded data corresponding to positions. With this method,according to step (e₄), a position may thereby be assigned to eachdetected optical code.

By assigning a specific position of the diffractive support andtherefore of other components permanently attached to said support, itis possible to enable and/or disable various functions orfunctionalities. The latter are for example involved in the handling andcontrolling of the operation of a vehicle.

In an exemplary embodiment, the information that is indicative of thequality of the signal may include error detecting and correcting codessuch as parity codes, information facilitating checksum operations, andinformation facilitating polynomial redundancy checks. For example,parity (even or odd) codes enable the counting of the quantity of “ones”in a word, and a parity code is indicative of whether there are an evenor odd number of “ones.” In an embodiment utilizing a parity code as anindication of quality, the receiving system may count the number of onesand compare the resulting count to the parity bit. In such a system, adisagreement may indicate an error and thus the system may assess thesignal as unreliable (i.e., exhibiting poor quality). It should be notedthat this method can detect single-bit errors and some multiple biterrors, but may be unable to correct the signal or otherwise improve itsquality without additional means for doing so.

The information that is indicative of the quality of the signal may alsoinclude information facilitating checksum operations. Checksums can beused on groups of data words wherein the sum of the data words iscalculated and stored with the data. In such systems, the receivingsystem calculates the same checksum and compares it with the receivedchecksum. In such a system, a disagreement may indicate an error andthus the system may assess the signal as unreliable (i.e., exhibitingpoor quality).

The information that is indicative of the quality of the signal may alsoinclude information facilitating cyclic redundancy checks usingpolynomials. In such systems, complex polynomials may be utilized thatcan not only detect, but in some cases correct, single- or multiple-biterrors.

It should be noted that error detection may be implemented in a digitalsystem through the use of error detecting codes and error correctingcodes. These codes may involve inserting redundant information into asequence of digital numbers. The redundant information is calculatedaccording to specific rules that allow errors of a certain magnitudewithin the sequence to be detected, and in some cases, corrected.Examples of error detecting and correcting codes include: even parity,odd parity, checksums, and Cyclic Redundancy Checks (CRC).

In accordance with the invention, an error detecting or error correctingcode may be included within each Computer Generated Hologram on thesensor disk. In this approach, each position encoded within the diskincludes redundant information that facilitates execution of an errordetecting or error correcting algorithm. Such algorithms enable theself-diagnosis of a wide variety of transient or permanent errors, andin some cases, facilitate the correction of those errors.

A particularly unique aspect of this implementation involves takingadvantage of the fact that this is a position sensor, and that a timesampling of positions reveals that these are not a random sequence ofnumbers. Specifically, if the disk is at position θ1 at time t1, then ifit is sampled again a very short time later, then θ1−Δ<θ2<θ1+Δ, where Δis the maximum amount the position can change during the time interval.Therefore, even if a relatively simple error detecting code is utilized,such as parity, then there is the opportunity to do internal correction,at least to some level of degraded accuracy.

In practice, it is recognized that in order to smoothly transition fromone position to the next in the digital realm, a gray code is used toencode the position information. A gray code is devised so that eachtransition from one position to the next involves a change in only onebit. An example 3-bit gray code sequence is:

-   -   000, 001, 011, 010, 110, 111, 101, 100

Assuming that a parity bit is used to detect an error in this 3-bitcode, and an error was detected when the previously read position was010, if the Δduring the sampling interval is 1, then the next readingwould have to be either 011 or 110. If the value reported was 001, thenknowing that parity detects a single bit error means that the true valuemust have been 011. Other logical deductions are also possible, giventhe various patterns that are possible.

According to an alternative application of the method according to theinvention, it is possible, prior to the comparison step (e₃) with amemory table, to proceed with a step for validating (e′₂) detection andreading. With this, it may notably be checked whether detection andreading were carried out under proper conditions not affecting theaccuracy of the result of reading.

According to an alternative embodiment of the method, by assigning aposition to the diffractive support (1), it is possible to enable ordisable functions or functionalities for information purposes. Forexample, here, these are indicative functions providing return ofinformation to the user.

According to still another embodiment of the method, assigning theposition may quite simply result, according to step (e₆), in storing thenew position, thereby detected and read. The cycle for determining theposition may resume according to a pre-established frequency.

The present invention also relates to a calculation algorithm, a flowchart of which is e.g. schematized as an example in FIG. 2. Thisalgorithm comprises a series of instructions I1, I2, I3, I4, I4, I5being used for applying the determination method according to theinvention. The first instruction I1 is directed to detecting theproperties of diffracted light spots or optical structures. According toa second instruction I2, the algorithm allows an electronic status to beassociated with each diffracted optical code. According to a followinginstruction I3, the diffracted optical code read by the detectors isthen processed by calculation means, so as to be able to convert it intoa distance or an angular deviation according to an instruction I4.According to another instruction I5, this distance or angular deviationis stored.

An exemplary diffractive support (1) according to the invention is forexample illustrated in FIG. 3 a or in FIG. 3 b. Said diffractive supportincludes means for mounting on a first component in relative motion withrespect to a second component, as well as at least one diffracted track(2, 3) either continuous or not. The diffractive tracks (2) or (3) havediffracting means by reflection and/or by transmission of the lightemitted by at least one light source, fixed relatively to the secondcomponent.

The diffractive support (1) for example includes a rigid disk and ameans for mounting (1 a) it on a rotary shaft as well as at least onering-shaped diffractive track (2) or (3) extending over 360°. Thediffractive tracks (2) or (3) for example have a relief etched into theconstituent material of said support (1), the reading of which allowsthe position of the first component (i.e. the diffractive support) to beidentified relatively to a second component (fixed mark). Thediffractive support (1) consists of a synthetic material of thepolycarbonate, PMMA (polymethyl methacrylate) type or of any otherorganic material having adequate optical properties.

The diffractive tracks (2) or (3) may also be obtained with an opaquematerial added to certain locations on a transparent support. The lightintensity of the wave front diffracted by the diffractive support andfocused on the detection means is read. The reading allows the positionof the first component to be identified relatively to the secondcomponent. The relief or the opaque material, the shape and distributionof which are calculated by computer, generate a particular diffractedoptical signal under the action of a light source, said signal being anoptical code defining a particular position of the support. Each track(2, 3) is divided into areas of individualized diffractive structures(4, 5) for example illustrated in FIGS. (4 a) and (5 a), and generatinga code corresponding to a unique position of the support (1).

The diffractive tracks (2, 3) may also be produced with transparency orrefractive index modulation.

FIG. 3 b shows an exemplary embodiment in which the rigid disk onlyincludes a single diffractive track (2). The latter may however consistof several adjacent diffractive annular sectors.

It has been noted that the disks, as well as some of the components, maybe subject to error due to manufacturing imperfections, dirt, damage ordegradation. It has also been noted that other potential sources of biterrors include manufacturing imperfections in the encoded disk, damageoccurring after manufacture, accumulation of foreign matter such as dirton a lens, mirror, or sensing array, electrical noise, abnormalities inthe signal processing algorithms that could cause misinterpretation of a1 or 0; and mechanical misalignment of the components.

It has also been noted that there are many places throughout a sensorsystem that are potential sources of error. These sources of errorinclude scratches, blemishes or other physical defects in the diskitself, scratches, blemishes or other physical defects in the detectorarray, electrical transients (noise) throughout the system, calculationerrors in the adaptive threshold algorithms or other parts of thesoftware, A/D conversion errors, and foreign contamination (dirt) of thesignal anywhere throughout the optical path. As a result of theserecognized sources of erroneous information, it has been found to bebeneficial to also include information that is indicative of the qualityof the optical signal or the resulting position information.

An example of each obtained code is for example materialized in FIGS. (4b) and (5 b). Each area of individualized diffractive structure forexample includes a plurality of elementary shapes positioned as a gridof these shapes, for example as 128×128 or 128×256. The optical signalforming the optical code defining a particular position of the supportrelatively to the beam, and examples of which are illustrated in FIGS.(4 b) and (5 b), for example consists of diffractive light spots (6, 7,8, 9), i.e., in the case in point, light spots of the first diffractionorder and, if necessary, of its conjugate (not shown). The followingdiffraction orders are not utilized but retained in the diffractedoptical signal. An exemplary first diffraction order is marked byreference 10 in FIGS. 4 b and 5 b. Without departing from the scope ofthe present invention, the use of the second diffraction order and, ifneed be, its conjugate order, may also be contemplated.

As an example, each diffracted track (2) or (3) is divided into angularsectors with equal surfaces forming the individualized diffractivestructures. For example the angular sectors have dimensions of the orderof 10 μm to 100 μm. Each diffracted track (2) or (3) preferablycomprises at least 3,600 angular sectors in order to obtain accuracyless than 0.1° in determining the position of the support.

According to an exemplary embodiment, for example illustrated in FIG.17, the diffractive track (2, 3) is positioned on a self-adhesivesupport. The latter may then be added, or more particularly adhered,onto any support and notably onto a support with a cylindrical aspect ofthe steering column shaft type. The dimensions of the diffractivesupport (1) may thereby be adapted to a location or to a particularshape. Reduced bulkiness and a large flexibility to use are obtained forthe diffractive support (1).

In FIGS. 6-9, four successive positions of a diffracting support,relatively to a fixed mark, have been schematized. This fixed mark ismaterialized by a fixed diaphragm and/or collimating unit (12)associated with the light source. The diffractive support (1) includesindividualized diffractive structures (13) and the displacement ismaterialized behind the unit (12) in FIGS. 6-9. With the methodaccording to the invention as illustrated in FIG. 6, it is possible toread a diffracted code (10) which varies according to the position ofthe individualized diffractive structure (13) and consequently of thediffractive support (1) relatively to the collimating unit. Thediffracted code (1) which corresponds to the first diffraction ordertherefore has a development transcribed via detection means with athreshold level, which measure light intensity variations for example.Three light spots reaching a maximum intensity level Imax as well as aspot without light are thereby obtained in FIG. 6. A code in the form of1 1 1 0 is thereby obtained via transformation means of theanalog/digital converter type. When the diffractive support (1)continues to rotate around its axis of rotation, an angular deviation ofthe individualized diffraction structure (13) is expressed by anotherlight distribution over the diffraction spots. Three light spots withreduced light intensity but with a level larger than the minimumdetection level Io, are thereby obtained. The fourth spot then passesfrom a spot without light to a spot with low intensity less than theminimum level Io. The thereby obtained digital optical code thus remainsunchanged. On the other hand, further rotation of the individualizeddiffractive structure (13) is expressed by a distribution of the lightintensity in the first diffraction order so as none of said light spotsare detected. The detected intensity actually is less than the minimumlevel Io. The optical code translated as 0 0 0 0, is thereby obtained.When the individualized structure (13) eventually is about to leave thecollimating window (12), a fourth light spot exceeding the minimumthreshold level Io is obtained, as well as three weaker light spots lessthan the minimum level Io and therefore being expressed by an opticalcode as 0 0 0 1. The 0 levels are very conspicuous and materialized bydotted lines in FIGS. 6-9 and levels 1 are materialized by bold lines.At each position of the diffractive support (1) and therefore in theindividualized diffractive structure (13), a unique optical code isthereby obtained according to a level of resolution determined by thesystem.

The present invention also relates to a device for measuring theposition of a first component in relative motion with respect to asecond component. Such a measuring device and more specificallydifferent alternative embodiments of this device are for exampleillustrated in FIGS. 10-17.

In the exemplary embodiment illustrated in FIG. 10, a steering column(20) is shown, onto which the diffracted support (1) is added. Thelatter for example has on its periphery a ring-shaped diffractive track(2). The diffractive support (1) is permanently attached to a rotaryshaft by any known means. The measuring device according to theinvention is positioned adjacent to the diffractive support (1) on afixed support (21). The measuring device includes a light source (22)emitting an incident beam (23 a) crossing the diffractive track (2). Theillustrated exemplary embodiment thus operates by transmission on thediffractive support (1). The incident beam (23 a) is diffracted at (23b) by the diffractive track (2). This diffracted beam (23 b) is thenguided via an assembly (24) for example including a wave guide andmirrors, towards detection means (25). The latter are controlled byadequate electronic means, with which the different optical codesdiffracted by the diffractive support (1) during its rotation may beanalyzed.

A set of gears (27) is also provided for driving a complementarydiffractive support at a different rotational velocity, thereby enablingthe number of revolutions to be counted and the absolute position to becoded over the whole steering wheel travel i.e., as a rule, plus orminus 4 or 5 revolutions.

In the exemplary embodiment illustrated in FIG. 11 a, the detection andreading means (25) are positioned at least partly directly under aperipheral area of the diffractive support (1). The light source (22)emits an incident beam (23 a) which is notably directed via a set ofmirrors (24) onto the upper surface of the diffractive track (2). Thediffracted code optical signal is then read by transmission under thediffractive support (1). This exemplary embodiment provides substantialreduction in bulkiness of the device according to the invention.

In the exemplary embodiment illustrated in FIG. 11 b, the diffractivesupport (1) is associated with a toothed wheel (28), which drives acomplementary set of gears (29).

A set of gears (29) is also provided, the function of which is identicalwith that of the set of gears (27).

As an example, the diffractive track may be directly added onto thetoothed wheel (28) which thereby forms the diffractive support.

According to another exemplary embodiment, the toothed wheel (28) ismade in a transparent material for the incident beam (23 a).

According to another exemplary embodiment for example illustrated inFIG. 12, the measuring device comprises an optical unit (30) with whicha diaphragm may be made in order to conform the incident optical beam(23 a).

According to another exemplary embodiment, illustrated in FIG. 13, thefixed light source (22) is associated with an optical guide (31) sendingthe light ray onto the diffractive track (2). The diffracted beam (23 b)is then read by the detection means (25) by transmission. The opticalguide (31) is for example made with optical fibers. The variability ofthe positioning of the light source (22) may thereby be substantiallyimproved without being detrimental to the performances and otheradvantages of the measuring device according to the invention, whichimparts greater flexibility to the assembly.

In the exemplary embodiment illustrated in FIG. 14, the diffractivesupport (1) is positioned under the toothed wheel (28). The fixed lightsource (22) is also positioned under the diffractive support (1) andemits an incident beam tilted relatively to the normal so as to obtain adiffracted beam directed towards the reading means (25). By selectingthe angle of incidence as well as by using a diffractive support byreflection, the positioning and the orientation of the fixed lightsource (22) on the one hand and of the reading detection means (25) onthe other hand, may be optimized.

According to another exemplary embodiment not illustrated in thefigures, it is also possible to provide a diffractive track (2)positioned on an annular section for example extending taperwiserelatively to the axis of rotation. With diffraction by reflection onthis tapered section including the diffractive track (2), it is alsopossible to optimize the positioning of the light source (22) on the onehand and that of the detection means (25) on the other hand.

According to another exemplary embodiment according to the invention andillustrated in FIG. 15, the steering column (20) is permanently attachedto a toothed wheel (33) and the diffractive support (1) is not directlymounted on said steering column (20). It is rotationally mounted on thefixed support (21) and driven into rotation by the toothed wheel (33)via an intermediate toothed wheel (34). A complementary toothed wheel,not illustrated, permanently attached to the axis of rotation of thediffractive support (1), is also provided. This complementary and axialtoothed wheel also drives a complementary set of gears (35), thefunction of which is identical with that of the set of gears (27).

The fixed light source (22) is positioned on the fixed support (21) andunder the diffractive support (1). The incident beam is therebydiffracted by the track (2) by transmission and guided via a set ofmirrors (24) towards the detection and reading means (25), which areassociated with electronic processing and analysis means (26) which arealso provided on said fixed support (21).

This exemplary embodiment of the device for measuring and determiningthe position of the diffractive support (1) has the advantage of mergingthe components of the device into a fixed sub-assembly adjacent to thesteering column (20). The thereby achieved sub-assembly may thus bemanufactured and assembled distinctly from the assembling of thesteering column (20).

Another exemplary embodiment according to the invention is for exampleillustrated in FIG. 16. In the latter, the incident beam (23 a) isdirected with a determined angle of incidence onto a mirror (36). Thelatter then redirects the incident beams (23 a) onto the diffractivetrack (2) which emits par transmission the diffracted beam towards thereading and detection means (25). By turning the mirror (36), it ispossible to optimize the relative positioning between the light source(22) and the reading and detection means (25).

The rotation of the diffractive support (1) also drives an additionalset of gears (37), the function of which is identical with that of theset of gears (27).

According to another exemplary embodiment illustrated in FIG. 17, thediffractive track (2) is directly added to the steering column (20) andmore particularly onto a cylindrical portion. The diffractive track isfor example added via a self-adhesive support onto this cylindricalportion. The light source (22) thus emits the incident beam (23 a)towards the diffractive track (2) along a direction extendingsubstantially in a plane normal to the axis of rotation R.

In such an exemplary embodiment, it is possible to position the lightsource (22) and the detection and reading means (25) away from thediffractive support (1) and consequently from the diffractive track (2).Such an embodiment has the advantage of reducing bulkiness to the extentthat it is not necessary to position the light source (22) or thedetection and reading means (25) below or above the diffractive track(2). In addition, the diffractive track (2) does almost not increase theradial bulkiness of the steering column (20). The latter is associatedwith a toothed wheel (38) as well as with an additional set of gears(39), the function of which is identical with that of the set of gears(27).

FIG. 18 illustrates an exemplary embodiment of a measuring deviceaccording to the invention. According to this exemplary embodiment, anincident beam (50) passes through a fixed diaphragm (51). The incidentbeam (50) is sent onto diffractive supports (52, 53) which may moveaccording to movements illustrated by the arrows D.

The incident beam is diffracted at (51) by the diffractive support. Itis then focused by the lens (55). Light spots (50 a, 50 b) correspondingto portions of the constituent signal of the selected diffraction orderand of its conjugate are thereby obtained in a plane (56) containingfixed detection means. Diffraction order 0 is marked on the optical axisAO with reference (58).

By referring to FIG. 19, an example of conformation of the incident beam(50) is seen for example.

The incident beam (50) thereby covers two distinct diffractive supports(1 c, 1 d). The diffractive supports (1 c, 1 d) include diffractivetracks (52, 53) with annular extension, respectively. The seconddiffractive support (1 d) in this case, for example by turning in thedirection R₂ at a lower velocity than the first diffractive support (1c) rotating in the R₁ direction, allows the number of revolutions to becounted for parts in relative rotation. A complementary diffractivetrack (59) is also provided on the first diffractive support (1 c)allowing light synchronization spots to be generated, as well as anothercomplementary diffractive track (60) allowing light calibration spots tobe generated for example.

According to FIG. 19, the incident optical beam (50), for example from alaser source, partially covers because of its conformation, thediffractive tracks (52, 53) for a specific position in a specificrotational revolution.

The basic geometrical shapes, constituent of the diffractive components,are recorded for example on computer files and are ready to bemanufactured for example by microlithography on a silicon, quartz, orglass wafer.

Other manufacturing methods may also be contemplated without departingfrom the scope of the present invention.

The diffracted optical signal according to the method in accordance withthe invention is illustrated as an example in FIG. 20. The latter showslight spots, the intensity of which is more or less intense, where thediffraction order 0 (58) localized on the optical axis AO, may beidentified as well as the first positive diffraction order (61 a) andthe first negative diffraction order (61 b).

Higher positive diffraction orders (62) as well as higher negativediffraction orders (63) are also illustrated, but are not considered inthe analysis of the diffracted optical signal.

FIG. 21 illustrates a detail of a diffracted optical signal created onthe detection means after focusing with the fixed lens (55). Withdifferent diffractive tracks, it is thereby possible to create a codedoptical signal on the detection means comprising a main coded signal(64) on 12 bits, synchronization signals (65) (light spots), and 4-bitoptical counting signals (66) reflecting the number of revolutionsaccomplished by one of the two components in relative rotation.

These diffracted optical signals are again found in the read-out arrays(67, 68) of the detection means. Optical calibration signals (69) arealso found on the detection array (68).

FIG. 21 also shows complementary diffracted optical signals (70), notconsidered in this example by the detection means, but being used foruniformizing the intensity of the detected light spots.

1. A diffractive support for applying the method according to claim 1,comprising: mounting means on a first component in relative motion withrespect to a second component; and at least one diffractive track;wherein said diffractive track has means diffracting the light beamemitted by at least one light source fixed relatively to the secondcomponent; wherein said diffractive track contains informationindicative of its quality.
 2. The diffractive support according to claim1, wherein the diffractive track has an etched relief in the constituentmaterial of said support capable of diffracting the incident beam(s) andof generating an optical signal, the reading of which allowing theposition of the first component relatively to the second component to beidentified, by identifying the code formed by the signal.
 3. Thediffractive support according to claim 1, wherein the diffractive trackis obtained by modulating the transparency of the support, for exampleby applying an opaque material at certain locations on a transparentsupport, in order to diffract the incident beam(s) and to generate anoptical signal, the reading of which allows the position of the firstcomponent relatively to the second component to be identified byidentifying the code formed by the signal.
 4. The diffractive supportaccording to claim 2, wherein the modulation of the reliefs or of thetransparency of the support, the distribution and geometry of which arecalculated by a computer, generates a particular diffracted opticalsignal under the action of at least one light beam, said signal formingan optical code consisting of optical structures defining a uniqueposition of the support at any time.
 5. The diffractive supportaccording to claim 1, wherein each track is divided into areas ofindividualized diffractive structures generating a code corresponding toa position of the support, each area including a plurality of elementaryshapes with a parallelogrammic aspect, positioned as a periodic oraperiodic grid.
 6. The diffractive support according to claim 1, furthercomprising: a rigid disk; a means for mounting said disk to a rotaryshaft; and at least one ring-shaped diffractive track.
 7. Thediffractive support according claim 5, wherein each track is dividedinto angular sectors with equal surfaces forming the individualizeddiffractive structures.
 8. The diffractive support according to claim 7,wherein the angular sectors have dimensions of the order of 10 μm to 100μm.
 9. The diffractive support according to claim 7, wherein at leastone track comprises 4,096 angular sectors.
 10. The diffractive supportaccording to claim 6, wherein the disk includes at its periphery, atapered portion, one of the tilted surfaces of which includes at leastone diffractive track.
 11. The diffractive support according to claim 1,wherein the diffractive track is positioned on a flexible support whichmay be adhered to a rigid component.
 12. A device for measuring theposition of a first component in relative motion with respect to asecond component, with a diffractive support according to claim 1,further comprising: at least one fixed light source, emitting at leastone light beam onto at least one mobile diffractive support; means fordetecting and reading an optical signal obtained by diffraction of thelight beam(s) by transmission or reflection from the diffractivesupport(s), wherein said optical signal contains information indicativeof its quality; and means for processing the optical code resulting fromthe detected signal allowing the position of the diffractive support(s)relatively to the beam(s) and the reliability of the positioninformation to be determined.
 13. The measuring device according toclaim 12, further comprising means for assessing the reliability of theposition information.
 14. The measuring device according to claim 12,further comprising means for correcting the position information. 15.The measuring device according to claim 14, wherein the coherent lightsource is a laser diode.
 16. The measuring device according to claim 12,wherein the light beam is sent towards the diffractive support via atleast one optical relay component of the lens, prism, diffractivecomponent, reflective component, refractive component type and/or via atleast one optical guiding component of the optical fiber or waveguidetype.
 17. The measuring device according to claim 12, wherein the beamis towards the diffractive support via at least one unit exerting acollimation, focusing or astigmatism function.
 18. The measuring deviceaccording to claim 12, wherein the light beam is towards the diffractivesupport via at least one conformation diaphragm.
 19. The deviceaccording to any of claim 12, wherein the means for detecting andreading diffracted optical codes consist of photodetectors of the type,array strips or pixel matrices, CCD sensors, photodiodes, or evenphotoelectric or photovoltaic cells positioned on the trajectory of therays diffracted by the diffractive support.
 20. The measuring deviceaccording to claim 19, wherein the photodetectors are positioned so thateach diffracted optical structure obtained at the location where adiffracted ray encounters a pixel array, covers at least 3 pixels. 21.The device according to claim 19, wherein the number of pixels betweentwo adjacent spots is set to at least 3 pixels.
 22. The device accordingto claim 12, wherein the light beam is directed at an incidence normalto the diffractive support.
 23. The device according to claim 12,wherein the light ray is tilted towards the diffractive support, by anangle between 0° and 17°, relatively to the normal to the diffractivesupport.
 24. The device according to claim 12, further comprisingsynchronization means for detecting and reading an optical codegenerated by an individualized diffractive structure when the beamemitted by the light source is centered on said structure.
 25. Themeasuring device according to claim 24, characterized in that thesynchronization means include specific photodetectors dedicated todetecting optical structures obtained independently of those forming thecode of the position to be measured, for example light spots positionedon at least one diffractive track specifically dedicated tosynchronization.
 26. The measuring device according to claim 12, whereinthe device is configured to facilitate measurement of the rotarymovement applied to at least one diffractive support permanentlyattached to a rotary shaft.
 27. The measuring device according to claim26, comprising two superimposed diffractive rotary disks, one includingthe measurement of angular positions on one revolution and the other,rotating N times less rapidly, allowing the number of accomplishedrevolutions to be measured within the limit of N revolutions.
 28. Themeasuring device according to claim 12, wherein a single componentforming an optical guide simultaneously acts as a diaphragm, acollimating lens, mirror(s), a protective housing for the laser diodeand the photodetectors.
 29. A method for calculating the position of acomponent with respect to another one from an optical code formed by aphoton signal generated by a diffractive support, said signal generatinga code consisting of optical structures with variable intensity,distributed over detection means, comprising: detecting the status ofeach optical structure and assigning it an electronic statecorresponding to its intensity; calculating the value of the code of themeasured position; assessing the quality or reliability of said valueand converting said code into a distance
 30. A steering column of avehicle comprising a position-measuring device according to claim 12.